Smallpox (variola major) continues to be a significant potential bioterror threat and preparation is of high priority because the consequences of a bioterror attack could be dire. Although adequate supplies of vaccine are available, over 40 million people are not good candidates for vaccination because of skin diseases, immunosuppression and heart disease. A safe, effective oral drug could be an important addition to the country's biodefense armamentarium. We previously discovered orally active analogs of cidofovir (CDV) which prevent death in lethal challenge models of poxvirus disease. One of these, hexadecyloxypropyl-CDV (HDP-CDV), has been chosen by NIAID for development with Phase I clinical trials targeted for early 2005. HDP-CDV and similar compounds prevent mortality and eliminate virus from liver and spleen in cowpox, vaccinia and ectromelia. However, HDP-CDV does not reduce lung viral titers, a potential drawback, since recovering persons might still harbor a million pfu of virus/gm of lung, raising the question of whether virus could still be transmitted by coughing. We have discovered that esterification of CDV with 1-O-octadecyl-2-O-benzyl-sn-glycerol (ODBG-) produces a very active antiviral which delivers 10 times more drug to lung than HDP-CDV. Lung-targeted antivirals like ODBG-CDV might solve the problem of high poxvirus titers in lung, while still providing excellent protection against lethal poxvirus challenge. This R21 project will explore this novel new type of prodrug; ODBG- analogs of CDV and the more active (S)-HPMPA and PMEG derivatives will be synthesized and evaluated. Their in vitro antiviral activity against cowpox, vaccinia, ectromelia, monkeypox and variola will be assessed and their cellular metabolism, oral pharmacokinetics and short term toxicology will be examined in mice. Dosing regimens will be developed and their activity will be compared with HDP-CDV in oral treatment of cowpox, vaccinia and ectromelia lethal challenge models in mice. [unreadable] [unreadable]